Question

I’m working on VS2010 c#.

I have a datatable containing username and passwords:

____________
andy | 1234
joni | 5678
lara | 4567

How do I form a function that will see what the user entered in a textbox and review if it is in the database or not?

Answer 1

You could write a SQL Function and do something like:

CREATE FUNCTION [dbo].[CheckUserExists] (@User NVARCHAR(50))
RETURNS BIT
AS 
BEGIN
DECLARE @RetVal INT

SELECT @RetVal = COUNT(User.UserId)
FROM
    Users
WHERE
    Users.Username = @User

IF @RetVal > 0 
BEGIN
   RETURN 1
END
    RETURN 0
END

Then in your C# program you could use ADO.NET and do:

private bool UserExists(string username) {
     SqlCommand cmd  = new SqlCommand("CheckUserExists", conn);

 cmd.CommandType = CommandType.StoredProcedure;

 cmd.Parameters.Add(new SqlParameter("@User", username));

     SqlDataReader reader = cmd.ExecuteReader(); // execute the function

     // return the response from the reader (1 if it is true, 0 for false)
}

You could then call the function by doing:

 var userExists = UserExists("YourUser");

http://www.csharp-station.com/Tutorials/AdoDotNet/Lesson07.aspx